In order to control particular objects (e.g., products), each object is provided with a unique code (e.g., a one dimensional code or two dimensional code showing the information identifying the product) for differentiating each product. By reading the unique code provided on the particular product with a code reader for comprehensively controlling the product.
A code reader is described in Japanese Patent Laid-Open Publication No. H07-3266. The code reader described in Japanese Patent Laid-Open Publication No. H07-3266 includes a lens, a sensor, and a light source provided in a main body case for reading a code. The known code reader further includes an aperture provided on a reading side of the lens for reading the code. A surface of incident light diaphragm has camouflaged color (i.e., the surface has a color that reflects like, for example, white or yellow) which enables the diffusion of the light and the light from the light source is irradiated to light entrance diaphragm.
Another code reader is described in Japanese Patent Laid-Open Publication No. H10-111905. With the code reader described in Japanese Patent Laid-Open Publication No. H10-111905, a light source is provided in a case, the light from the light source is irradiated to the code, and the reflected light from the code is read by a camera via an incidence diaphragm mechanism and a lens. This code reader further includes a semi-transparent mirror plate between the lens and a reading side. The semi-transparent mirror plate is provided with an inclination. The light source corresponds to a plane illuminant generating the diffused light. With the known code reader, the plane illuminant is positioned for irradiating the light to the semi-transparent mirror plate. According to the known code reader disclosed in Japanese Patent Laid-Open Publication No. H10-111905, the semi-transparent mirror plate is equipped on end portions of the case body and the light entrance diaphragm mechanism having the inclination (i.e., angle of gradient being 45 degrees).
Notwithstanding, the light irradiated from the light source is absorbed by the camouflaged colored incident diaphragm and thus fails to produce the diffused light with sufficient luminance with the known code reader disclosed in Japanese Patent Laid-Open Publication No. H07-3266 because the surface of the incidence stop has camouflaged color which enables the diffusion of the light and the light source is irradiated to the light entrance diaphragm. Accordingly, in case the diffused light irradiated to the code is insufficient, the sufficient reflective light cannot be incident to the sensor, and, as a result, the recognition accuracy of the code is declined. In this case, the light source with high luminance may be applied or the output of the light source may be increased in order to ensure sufficient luminance of the diffused light. However, with this construction, a drive circuit of the light source is complicated, plural light sources are required, or the precious light source has to be applied, all of which increase the manufacturing cost.
The code reader described in Japanese Patent Laid-Open Publication No. H07-73266 includes the following drawbacks. For example, in case a code is provided on a mirror surface, although the incidence diaphragm mechanism has the camouflaged color such as white, a light entrance hole (i.e., entrance pupil) to which the light of the incidence diaphragm mechanism irradiates is darker than surroundings of the camouflaged color portion.
Accordingly, the dark portion (referred as a “black point” hereinafter) of the light entrance hole appears on the code of the mirror surface when reading the code provided on the mirror surface, and the black point is recognized by the sensor. Thus, when the black point appears on the code provided on the object, the reading accuracy of the code reader is reduced due to the black point to deteriorate the code reading. Thus, with the code reader described in Japanese Patent Laid-Open Publication No. H07-73266, the code has to be read by adjusting the position of the code reader relative to the code so that the black point does not overlap the code. This deteriorates the operability of the code reader when reading the code.
On the other hand, the length from the incidence diaphragm mechanism to the reading side is elongated with the code reader described in Japanese Patent Laid-Open Publication No. H10-111905, because the semi-transparent mirror plate is provided between the light entrance diaphragm mechanism and the reading side and because the reading side is provided having closed inclination by 45 degrees for blocking the light entrance diaphragm mechanism (to prevent dust from entering the lens) in the lens in order for the light being incident from other directions. This increases the size of the code reader.
In addition, because the semi-transparent mirror plate is equipped having the gradient angel of 45 degrees, the reflectance and the transmittance of the light is varied when the angle of gradient is changed. This influences on the brightness of the light reflected by the semi-transparent mirror plate. The change of the brightness of the light influences the recognition rate of the code.
Further, because one end portion of the semi-transparent mirror plate is equipped on the end portion of the case body, for example, in case the user drops the code reader on the ground, the impact from hitting on the ground is easily transmitted to the semi-transparent mirror plate. The mirror plate is therefore vulnerable to damage.
A need thus exists for a small and strong code reader which enables to read the code provided on a mirror surface with good operability to create the diffusion light with low manufacturing cost.